一元酸对乳酸缩聚的调聚作用

摘要

In order to control the polymerization degree and the structure of end groups in lactic polycondensation process,the two-stage direct polycondensation of lactic acid was studied under the conditions of adding chloroacetic acid,stearic acid or acetic anhydride.The structure of the products was characterized by 1 H NMR,and the mass measurement was used to track the reaction process.The experimental results show that the mass of reaction system continuously decreases and the decreasing tendency continuously weakens.The main mass reduction appears in the reflux reaction stage.The above mass change law has nothing to do with the kind of monocarboxylic acid.When the mass ratio of chloroacetic acid to lactic acid is 0.041 ∶ 1.00,the number-average polymerization degree of poly(lactic acid) is 45; When the mass ratio of stearic acid to lactic acid is 0.14 ∶ 1.00,the number-average polymerization degree of poly(lactic acid) is 16; When the ratio of acetic anhydride' s volume to lactic acid's mass is 0.05 mL ∶1.00 g,the number-average polymerization degree of poly(lactic acid) is 21.These results indicate that the polymerization degree and end group structure of product can be regulated when monocarboxylic acids were added in the course of lactic acid polycondensation,but the regulation effect is closely related to the structure and characteristics of monocarboxylic acids.%具有可控聚合度和端基结构的聚乳酸在精细化工、功能高分子领域具有重要应用.为了调控乳酸缩聚过程中的聚合度和端基结构,对添加氯乙酸、硬脂酸、乙酸酐等一元酸的乳酸两阶段直接缩聚进行了研究.通过1 H NMR对产物的结构进行了表征,通过质量测定对反应过程进行了跟踪.实验结果表明,无论在哪种一元酸存在条件下,反应过程中质量不断减少且减少趋势随聚合时间增加而减弱,主要的质量减少出现在回流反应阶段.氯乙酸与乳酸的质量比为0.041∶1.00时,聚乳酸的数均聚合度为45；硬脂酸与乳酸的质量比为0.14∶1.00时,聚乳酸的数均聚合度为16；乙酸酐的体积与乳酸的质量比为0.05 mL∶1.00 g时,聚乳酸的数均聚合度为21.表明添加一元酸对乳酸缩聚产物聚合度和端基结构具有调节作用,但调节的具体结果与一元酸的结构和特性密切相关.